LCDs are widely used in various modern information products, such as notebooks, personal digital assistants, video cameras and the like.
When motion pictures are introduced to an LCD, an image of the previous frame may remain in visual perception of a viewer as an afterimage. The afterimage overlaps with an image of the current frame in the perception of the viewer. This causes a so-called residual image phenomenon to be generated, accordingly a display quality of the LCD is impaired. To overcome the above-described problem, a method called as black insertion driving is provided to drive the LCD.
FIG. 7 is an abbreviated circuit diagram of a conventional LCD, which is capable of utilizing the black insertion driving method. The LCD 100 includes a liquid crystal panel 101, a scanning circuit 102, and a data circuit 103. The scanning circuit 102 and the data circuit 103 are configured for driving the liquid crystal panel 101.
The liquid crystal panel 101 includes n rows of parallel scanning lines 110 (where n is a natural number), m columns of parallel data lines 120 orthogonal to the n rows of parallel scanning lines 110 (where m is also a natural number), and a plurality of pixels 130 cooperatively defined by the crossing scanning lines 110 and data lines 120. The scanning lines 110 are electrically coupled to the scanning circuit 102. The data lines 120 are electrically coupled to the data circuit 103.
Each pixel 130 includes a thin film transistor (TFT) 131, a pixel electrode 132, a common electrode 134, and liquid crystal molecules (not labeled) interposed between the pixel electrode 132 and the common electrode 134. The TFT 131 is disposed near an intersection of a corresponding one of the scanning lines 110 and a corresponding one of the data lines 120. A gate electrode of the TFT 131 is electrically coupled to the corresponding one of the scanning lines 110, and a source electrode of the TFT 131 is electrically coupled to the corresponding one of the data lines 120. Further, a drain electrode of the TFT 131 is electrically coupled to the pixel electrode 132. The common electrode 203 is electrically coupled to a common voltage generating circuit (not shown) that is configured to provide common voltages. Moreover, each pixel electrode 132, the corresponding common electrode 134, and the liquid crystal molecules therebetween cooperatively form a liquid crystal capacitor 133.
When the LCD 100 is driven via the black insertion driving method, each frame period is divided into a first sub-frame period and a second sub-frame period. In particular, the first sub-frame period serves as a normal display period, and the second sub-frame period serves as a black frame insertion period.
During the first sub-frame period, a plurality of first scanning signals are generated by the scanning circuit 102, and are sequentially supplied to the scanning lines 110, so as to scan the corresponding pixels 130 row by row. When the corresponding row of pixels 130 is scanned by the first scanning signal, the TFTs 131 of the pixels are switched on. The data circuit 103 then supplies a plurality of first driving voltages to the pixel electrodes 132 of the pixels 130 via the data lines 120 and the TFTs 131, so as to charge the liquid crystal capacitors 133. Moreover, common voltages are applied to the common electrodes 134 of the pixels 130 by the common voltage generating circuit. Thereby, when the charging process is finished, an electric field is generated between the pixel electrode 132 and the common electrode 134 of each pixel 130, and the electric field is retained until the pixel 130 is scanned once again in a following sub-frame period. The electric field drives the liquid crystal molecules of the pixel 130 to tilt to a corresponding angle, so as to control the light transmission of the pixel 130. Accordingly the pixel 130 displays an image unit having a corresponding gray level.
After the last row of pixels 130 are scanned and the liquid crystal capacitors 133 thereof are charged, the first sub-frame period is finished and the second sub-frame period starts thereafter.
During the second sub-frame period, the scanning circuit 102 supplies a plurality of second scanning signals to switch on the TFTs 131 of pixels 130 row by row. The common voltages are kept on providing to the common electrodes 134. The data circuit 103 supplies a plurality of second driving voltages having values the same as that of the corresponding common voltages to the pixel electrodes 132 of the pixels 130. This causes the liquid crystal capacitor 133 of each pixel 130 to be discharged. When the discharging process is finished, the electric field is removed. Thereby, the liquid crystal molecules of the pixel 130 return to the original positions, so as to prevent light beams from transmitting therethrough, such that each pixel 130 of the LCD 100 displays a black image unit. That is, a sub-frame of black image is inserted between two successive sub-frames of normal images.
By employing the black insertion driving method, normal images and black images are displayed alternately. In a complete frame period, a viewer perceives the normal image during the first sub-frame period, and perceives the black image during the second sub-frame period. Thus an afterimage of the image displayed in the first sub-frame period is removed from the perception during of the viewer in the second sub-frame period. This means that the problem of the residual image phenomenon can be solved.
However, when the LCD 100 displays a still image in a plurality of sequential frames period, the alternation of the normal image and the black image may cause a so-called flicker phenomenon to be generated. A viewer may perceive that the image displayed in the LCD 100 is skipping or jumping. This causes the display quality of the LCD to be low all the same.
It is, therefore, desired to provide an LCD and a method for driving the LCD which overcome the above-described deficiencies.